A middleman is someone who buys products in bulk and resells them to a retailer. Middlemen are often often confused with wholesalers but there is a real difference between a wholesaler and a middleman!
Middlemen often pose as wholesalers but are actually light bulk distributors who buy in small to medium bulk from bulk wholesalers. Middlemen cannot offer the same discounted prices on goods like wholesalers can.
In recent times, many legitimate wholesalers have been mistakenly labelled as middlemen because when retailers compare prices of items on eBay and the prices that wholesalers can offer, it's often cheaper to buy on eBay! This is usually because the eBay seller is a wholesaler themselves who buys direct from the manufacturer.